Biology lecture 1 The E.coli Cell Gene expression Feedback And Control Quorum Sensing Taxis Global Control Enzyme Regulation

The E.coli Cell Cell Wall Cytoplasm No ER or Golgi therefore most mammalian proteins cannot be expressed by Bacteria due to lack of post translational modification DNA

Cell Wall Structure Phospholipid Bi-layer (Plasma Membrane) Peptidoglycan Phospholipid

The Cell wall in gram negative bacteria (like E.coli) Passive Transport Protein Outside Has no access to proton gradient or ATP Has proton Gradient and access to ATP Active Transport Protein Inside

Plasmids Present in nature Exchanged by competent bacteria Encode genes DNA

Gene Control Transcriptional regulation Translational Control Protein Stability DNA mRNA Protein mRNA stability Control DNA structural Control Activation eg. Phosphorolation Functional Protein

A Gene and Controll P R P O A B C R R I R I +

Ara BAD Operon + C PC P O I B A D P2 P1 Operator Promoters Inducer Arabinose

Transcription Initiation Polymerase Inducer DNA This is Very Complicated we hide this complexity in a black box but it can affect the performance of our devices so you should know that it exists

Any form of gene control you can imagine Multiple RBS Multiple Promoters Multiple inhibitors Feedback loops, ie inhibitor under the control of it’s promoter

Two Component Systems External Signal Binds DNA Membrane Bound Component (sensor) P P ATP Binds DNA P ADP P Intracellular Component (Transcriptional Regulator)

Quorum Sensing Allows Cell-Cell communication Shows a Threshold Response Lux R Lux Genes Lux I + -

Taxis Bacteria can move towards an attractant or away from a repellent Attractants include Chemicals Light Magnetism Take Multiple readings using an analogue system Remember previous readings Move by a biased Random Walk

Global Control Stimuli Effects are massive 150+ genes activated / inhibited per stimulus Most operators / inhibitors are affected by a global control mechanism Eg. Presence of Glucose is a stimulus for a global control mechanism so if a bacteria is grown on a glucose medium the araBAD operon will not initiate transcription.

Enzyme Regulation C B A E1 E2 Inhibition Activation No DNA, no translation, no transcription therefore very fast Very hard to engineer and much less flexible than the systems mentioned earlier Usually involved in central pathways therefore interference is likely

Any Questions?